1. Field of the Invention
The present invention relates in general to a lift device of a laser disc player and, more particularly, to a lift device of a laser used for maintaining a predetermined gap between an objective lens of a pick-up unit and a disc.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a construction of a typical lift device of a laser disc player. As shown in this drawing, the typical lift device includes a spindle motor 1 for rotating a disc D, a turntable (not shown) for seating the disc D thereon, a clamp mechanism 3 for clamping the disc D and rotating together with this disc D, and a pick-up unit 4 having an objective lens L. The lift device further includes a rack 5 for moving the pick-up unit 4 in a radial direction of the disc D, and a lift mechanism for maintaining a predetermined gap between the objective lens L of the pick-up unit 4 and the disc D. The lift mechanism is so constructed that it couples one end of the rack 5 to a hinged part 6 and drives a cam 7 provided on a lower surface of the right-side section of the rack 5, thus to adjust the height of the pick-up unit 4.
In play mode of the laser disc player, the pick-up unit 4 of the lift device moves along the rack 5. In this case, it is required to precisely maintain the predetermined gap between the objective lens L of the pick-up unit 4 and the disc D in order to correctly read the information stored in the disc D. However, the typical lift device can not reliably maintain the predetermined gap between the objective lens L and the disc D since the rack 5 has a longer length and the pick-up unit 4 has a heavy weight. There has been proposed a pick-up device (not shown) which can closely adjust the gap between the objective lens L of the pick-up unit 4 and the disc D. However, this pick-up device has a problem that it is only used in close adjustment of the gap between the lens L and the disc D, but fails in maintaining of the predetermined gap between the lens L and the disc D in the case of use of large-sized disc.
On the other hand, the typical laser disc D may be bent due to its size and this bending of the disc D causes the laser beam emitted from the objective lens L of the pick-up unit 4 to fail in its vertical incidence on the disc D. In order to overcome the problem caused by failure in vertical incidence of the laser beam on the disc D, a tilt operation is required. However, such a tilt. operation is attended with variation of the distance between the disc surface and the objective lens L of the pick-up unit 4, so that the above tilt operation should be accompanied with a lift operation to compensate for the variation of distance. However, the typical lift device of the laser disc player, while carrying out the lift function, nevertheless has a problem that it achieves no precision in its operation since the relatively longer rack 5 is moved by the cam 7. Another problem of the typical lift device is that it cannot stand up well to external shock and vibration.